1. Field of the Invention
The present invention relates a method and an apparatus for peeling a lens sheet such as a Fresnel lens sheet from a forming mold.
2. Description of the Related Art
Japanese Laid-Open Patent Application Nos. S64-86102, H6-67002 and H7-148751 disclose a method for manufacturing various kinds of lens sheet such as Fresnel lens sheets, lenticular lens sheets or the like, which are to be used for a transmission type screen for a projection TV.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. S64-86102, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming mold to form an uncured resin layer. Then, the ultraviolet ray curing type resin in the form of liquid is applied on one side of the uncured resin layer to form an uncured resin pool. Then, a sheet-shaped substrate is placed on the uncured resin pool. The uncured resin pool and the uncured resin layer are pressed together with the substrate against the forming mold by means of a pressing roller from the above-mentioned one side of the uncured resin layer toward the other side thereof so as to obtain a laminate structure of the substrate and the ultraviolet ray curing type resin, while excluding bubbles from the ultraviolet ray curing type resin. Then, ultraviolet ray is irradiated on the ultraviolet ray curing type resin through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming mold, thus manufacturing a lens sheet.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. H6-67002, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming mold to form an uncured resin layer. Ultraviolet ray is irradiated on the uncured resin layer to cure it. The ultraviolet ray curing type resin is further applied on one side, i.e., a pressing-starting side of the cured resin layer to form an uncured resin pool. Then, the thus applied ultraviolet curing type resin is spread through a sheet-shaped substrate into a uncured resin layer by means of a pressing roller so as to obtain a laminate structure of the substrate, the cured resin layer and the uncured resin layer, while excluding bubbles from the ultraviolet ray curing type resin. Then, the ultraviolet ray is irradiated on the uncured resin layer through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming mold, thus manufacturing a lens sheet.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. H7-148751, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming mold to form an uncured resin layer. Solvent contained in the ultraviolet ray curing type resin is vaporized by a hot-air dryer to form a solvent-vaporized layer. Then, the ultraviolet ray curing type resin is applied on one side, i.e., a pressing-starting side of the solvent-vaporized layer to form an uncured resin pool. Then, the uncured resin pool is spread through a sheet-shaped substrate into a uncured resin layer by means of a pressing roller so as to obtain a laminate structure of the substrate, the solvent-vaporized layer and the uncured resin layer, while excluding bubbles from the ultraviolet ray curing type resin. Then, the ultraviolet ray is irradiated on the uncured resin layer through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming mold, thus manufacturing a lens sheet.
However, the above-mentioned prior art has a problem that the lens sheet may be damaged when being peeled from the forming mold.
An object of the present invention is therefore to provide a method and an apparatus for peeling a lens sheet from a forming mold, which provide a reliable peeling of the lens sheet without causing damage.
In order to attain the aforementioned object, the method of the first aspect of the present invention for peeling a lens sheet having two pairs of opposite portions from a forming mold, comprises:
a first peeling step for pulling up a pair of opposite portions of a lens sheet, which is formed on a forming mold, to peel partially said lens sheet from said forming mold;
a second peeling step for pulling up an other pair of opposite portions of said lens sheet to peel partially said lens sheet from said forming mold; and
a third peeling step for pulling up further said two pairs of opposite portions to peel entirely said lens sheet from said forming mold.
In the second aspect of the present invention, said first peeling step and said second peeling step may be conducted simultaneously.
In the third aspect of the present invention, said first peeling step and said second peeling step may be conducted at a different time.
In the fourth aspect of the present invention, said first peeling step may be conducted by pulling up said pair of opposite portions simultaneously; and said second peeling step may be conducted by pulling up said other pair of opposite portions simultaneously.
In the fifth aspect of the present invention, said first peeling step may be conducted by pulling up said pair of opposite portions simultaneously; and said second peeling step may be conducted by pulling up said other pair of opposite portions at a different time.
In the sixth aspect of the present invention, said first peeling step may be conducted by pulling up said pair of opposite portions at a different time; and said second peeling step may be conducted by pulling up said other pair of opposite portions simultaneously.
In the seventh aspect of the present invention, said first peeling step may be conducted by pulling up said pair of opposite portions at a different time; and said second peeling step may be conducted by pulling up said other pair of opposite portions at a different time.
According to the above-mentioned features of the first to seventh aspects of the present invention, it is possible to peel smoothly the lens sheet from the forming mold, while preventing irregularities formed on the lens sheet from being coming into frictional contact with or being caught by irregularities of lens formation grooves of the forming mold. Defects or damage of the lens sheet can be prevented.
In the eighth aspect of the present invention, the method thereof may further comprise a holding step for holding a central portion of said lens sheet on said forming mold, prior to said first peeling step. According to such a feature, it is possible to peel the lens sheet from its periphery toward its central portion, thus preventing the peeling action starting from a certain peripheral position from extending through the central portion of the lens sheet to the opposite side. As a result, it is possible to reliably prevent the irregularities formed on the lens sheet from being coming into frictional contact with or being caught by the irregularities of the lens formation grooves of the forming mold.
In the ninth aspect of the present invention, said pair of opposite portions may be a pair of opposite diagonal edge portions of said lens sheet and said other pair of opposite portions may be the other pair of opposite diagonal edge portions thereof. According to such features, it is possible to catch the lens sheet to pull it up, thus performing an easy peeling operation of the lens sheet.
In the tenth aspect of the present invention, said pair of opposite portions may be a pair of opposite side portions of said lens sheet and said other pair of opposite portions may be the other pair of opposite side portions thereof. According to such features, it is possible to prevent deformation of the lens sheet when peeling it from the forming mold.
In the eleventh aspect of the present invention, said first peeling step may comprise a plurality of first sequential sub-steps for pulling up said pair of opposite portions by a first prescribed pulling stroke; said second peeling step may comprise a plurality of second sequential sub-steps for pulling up said other pair of opposite portions by a second prescribed pulling stroke; and said first peeling step and said second peeling step may be conducted alternately. According to such features, it is possible to peel the lens sheet from the forming mold in an appropriate manner even when the lens sheet has a large size.
In the twelfth aspect of the present invention, said first prescribed pulling stroke may increase according as number of said first sequential sub-steps increases; and said second prescribed pulling stroke may increase according as number of said second sequential sub-steps increases. According to such features, the lens sheet is peeled gradually from the forming mold. It is therefore possible to prevent an excessively large force from being applied to the lens sheet when peeling the lens sheet, thus avoiding occurrence of defect or damage of the lens sheet.
In order to attain the aforementioned object, the apparatus of the thirteenth aspect of the present invention for peeling a lens sheet having two pairs of opposite portions from a forming mold, comprises:
a first lifting device for pulling up a pair of opposite portions of a lens sheet, which is to be formed on a forming mold;
a second lifting device for pulling up an other pair of opposite portions of said lens sheet; and
a control device for controlling said first and second lifting devices on a basis of any one of (i) a first operation mode that the pulling up of said pair of opposite portions of said lens sheet by said first lifting device and the pulling up of said other pair of opposite portions thereof by said second lifting device are conducted simultaneously to peel partially said lens sheet from said forming mold, and then both of said pair of opposite portions of said lens sheet and said other pair of opposite portions thereof are further pulled up by means of said first and second lifting devices to peel entirely said lens sheet from said forming mold, and (ii) a second operation mode that the pulling up of said pair of opposite portions of said lens sheet by said first lifting device and the pulling up of said other pair of opposite portions thereof by said second lifting device are conducted at a different time to peel partially said lens sheet from said forming mold, and then both of said pair of opposite portions of said lens sheet and said other pair of opposite portions thereof are further pulled up by means of said first and second lifting devices to peel entirely said lens sheet from said forming mold.
According to the above-mentioned features of the thirteenth aspect of the present invention, it is possible to peel automatically the lens sheet from the forming mold, while preventing occurrence of defects or damage of the lens sheet.
In the fourteenth aspect of the present invention, the apparatus may further comprise a holding device for holding a central portion of said lens sheet on said forming mold. According to such a feature, the holding device holds the central portion of the lens sheet on the forming mold. It is therefore possible to peel the lens sheet from its periphery toward its central portion, thus preventing the peeling action starting from a certain peripheral position from extending through the central portion of the lens sheet to the opposite side. As a result, it is possible to reliably prevent the irregularities formed on the lens sheet from being coming into frictional contact with or being caught by the irregularities of the lens formation grooves of the forming mold.
In the fifteenth aspect of the present invention, said first and second lifting devices may comprise a plurality of suction cups. According to such a feature, it is possible to catch the lens sheet to pull it up without causing occurrence of defects or damage of the lens sheet.
In the sixteenth aspect of the present invention, said first and second lifting devices may comprise a plurality of clamping members. According to such a feature, it is possible to catch firmly the lens sheet to pull it up.
In the seventeenth aspect of the present invention, said control device may control said first and second lifting devices so that a plurality of first sequential sub-steps for pulling up said pair of opposite portions by a first prescribed pulling stroke are conducted by said first lifting device, a plurality of second sequential sub-steps for pulling up said other pair of opposite portions by a second prescribed pulling stroke are conducted by said second lifting device, and said plurality of first sequential sub-steps and said plurality of second sequential sub-steps are conducted alternately. According to such features, it is possible to peel the lens sheet from the forming mold in an appropriate manner even when the lens sheet has a large size.
In the eighteenth aspect of the present invention, said control device may control said first and second lifting devices so that said first prescribed pulling stroke increases according as number of said first sequential sub-steps increases; and said second prescribed pulling stroke increases according as number of said second sequential sub-steps increases. According to such features, the lens sheet is peeled gradually from the forming mold. It is therefore possible to prevent an excessively large force from being applied to the lens when peeling the lens sheet, thus avoiding occurrence of defect or damage of the lens sheet.
The present invention includes possible combination of the above-described features of the aspects of the present invention. In the present invention, the xe2x80x9cforming moldxe2x80x9d means a device for forming or molding a lens sheet and includes a forming die.